I found a couple of articles which claim cloves have a preservative effect in foods and kept worms out, but they did not back it up with any research. But maybe the Boers found it helped to preserve the sausage.
"Clove has been used for centuries as a primary preservative as well as a flavoring agent for preserved foods. Before modern technology like refrigerators and stoves was available to prolong the life of food or preserve it through canning, most people relied on curing, smoking, pickling, and salting to make sure that their food would last during poor weather. Preserving food makes it inhospitable to microbes and effectively halts the rotting process. Cloves, which are the aromatic buds of a tree native to Indonesia, are high in antimicrobial, antifungal, antioxidant, and antilarval properties. The primary substance in cloves that makes it so great for preserving food is called eugenol. Because of its antimicrobial properties, in addition to its strong fragrance, eugenol may also be used in cosmetics as a preservative."
